LABORATORY AND FIELD EFFICACY OF NEEM (AZADIRACHTA-INDICA-A JUSS) EXTRACTS AGAINST 2 BROCCOLI PESTS

This study was conducted to test the growth-regulating activity of nee m extract on the cabbage webworm Crocidolomia binotalis Zeller (Lepido ptera: Pryralidae) and to evaluate the field efficacy of the extract a gainst the diamondback moth Plutella xylostella (L.) (Lepidoptera: Ypo nomeutidae) and against C. binotalis on broccoli plants. In the labora tory, third- and fourth-inst ar larvae of C. binotalis were fed brocco li leaves treated with neem extract or azadirachtin for 24 h and 48 h, respectively, and then their development: was followed until pupation or adult emergence. Metamorphic effects of neem extract on the fourth instar in the course of its development to the adult stage were class ified into five categories: 1) the fourth-instar larva died before or during pupation, 2) malformed pupa, 3) the larva successfully pupated but died before adult emergence, 4) malformed adult or the adult did n ot eclose completely from the pupal case, and 5) normal adult. The qua ntitative data for these effects were subjected to polytomous binary r esponse analysis based on the conditional binomial model. The results revealed that the conditional probability of occurrence of the effect in all categories was concentration-dependent, and this suggests that neem extract exerts strong metamorphic disturbances in the development of the test insect. The median moulting inhibitory concentration (IC5 0) of neem extract: and azadirachtin against the third instar was 0.27 % and 43.9 mu g/l, respectively, and that of neem extract against the fourth instar was 0.065 %. In the field, the treatment with neem oil (azadirachtin: 2.5 % w/v) at rates of 1.8, 2.4 and 3.0 l/ha provided c omparable protection to broccoli plants from infestation by P. xyloste lla as that with Sumicidin 200 EC (fenvalerate 50 g/ha). In addition, the same treatments could check, though not completely, the build-up o f C. binotalis population and markedly reduced the damage on broccoli heads.